1. Field of the Invention
The invention pertains to unfolding fins, such as those used in missiles, self-propelled rockets and similar devices which we shall hereinafter call guided missiles, and pertains especially to a system to brake the unfolding of these fins.
2. Description of the Prior Art
In the prior art, there are known unfolding fins hinged on the body of the missile, on longitudinal axes, parallel to the longitudinal axis of the body. These fins are tangential to the body in the folded position and are located in radial axial planes in the active position.
Another prior art system is described in French patent No. 1 485 580, which is an improved vane unit for rockets, in which each fin is hinged on the body of the vane unit around an oblique orientating axis. The effect of this is that, when the fins are being unfolded, each of them passes from a folded position in which it is applied tangentially to the body of the vane unit, into an unfolded position, in which the fin is located in a radial axial plane.
This type of vane unit has a major disadvantage owing to the suddenness with which the fins are unfolded. This movement is provoked mechanically either by pistons or by pyrotechnical devices which tend to move the fins away from the body of the missile. Once these fins are moved away, the increase in the velocity of the missile at the moment of unfolding and the increase in the rotational velocity of the fins, due to the increase in the area of the fin that is being unfolded, makes the latter reach its unfolded position at considerable velocity and hence with energy sufficient to damage either the fin itself or the limit stop elements which hold it in this unfolded position.
The invention proposes to remove this disadvantage by proposing a system to brake the unfolding of the fin to prevent this sudden stop in the unfolded position and, hence, to prevent damage to a set of fins mounted on a guided missile.
furthermore, French patent No. 2448707 describes a set of fins for a missile where a fin may rotate on an axis tangential to the body of the missile on a rotating plate which can itself rotate around an axis transversal to the missile. This rotation is done by worm screws which transmit the rotational motion to the rotating plate while the fin rotates around the tangential axis. The fin is first applied to the surface of the missile, its axis being pointed tangentially and transversally to the longitudinal axis of the missile. When it is being straightened, the fin rotates in such a way that its axis is parallel to the longitudinal axis of the missile. In this assembly, there is provision for a braking mechanism that acts on the rotating plate to delay the rotational movement of the said plate and, consequently, the unfolding of the fin.
This device has a drawback in that it brings far too many moving mechanical parts (rotating plate, worm screw, etc.) into play.